Regioselective nitration of diphenyl compounds

ABSTRACT

A regioselective nitration process for diphenyl compounds which can be carried out at about ambient temperature in which each ring of the diphenyl compound is selectively nitrated in the para position to form the corresponding di(4-nitrophenyl) compound. Such compounds as diphenyl carbonate, 2,2-diphenylpropane, 2,2-diphenylhexafluoropropane, diphenyl sulfide, diphenyl ketone, diphenyl sulfone, and the like can be converted to an isomeric mixture containing an enhanced amount of the corresponding di(4-nitrophenyl) compound, which mixture may be reduced or purified and reduced to the di(4-aminophenyl) analogues for use in the manufacture of polyamides, polyimides, and polyamide-imides.

This is a division of application Ser. No. 327,043, filed Mar. 22, 1989.

BACKGROUND OF THE INVENTION

This invention relates to the improved regioselective ambienttemperature nitration of diphenyl compounds in the presence ofnitrobenzene and, more particularly, to an ambient temperature nitrationprocess, which employs nitrobenzene as a nitrating solvent, of diphenylcompounds in which each phenyl ring is selectively nitrated in the paraposition to form a di(4-nitrophenyl) compound. When the selectivenitration process is combined with a novel regiopurification technique,essentially regiopure 2,2-di(4-nitrophenyl) carbonate can be made whichmay be decarboxylated and reduced to essentially regiopuredi(4-nitrophenyl) ether. The regioselective nitration process taughthere provides a convenient route to di(4-nitrophenyl) compoundsgenerally, such as 2,2-di(4-nitrophenyl)propane and its hexafluoroanalogue, compounds which can be reduced to the corresponding diaminesto be used in polyamides, polyimides, and polyamide-imides.

The commercial preparation of substituted diphenyl compounds such asdiphenyl ethers in which each ring is monosubstituted has becomeimportant because of the use of such materials, in particular, thediamino derivatives, in polyamides, polyimides, and polyamide-imides.Because of the multiplicity of regioisomers formable in the manufactureof such compounds and the difference in properties of materials madefrom the different isomers, it is of commercial importance to be able tocheaply produce highly regiopure compounds. In particular, it isimportant to be able to make highly regiopure 4,4'-compounds such asdi(4-nitrophenyl) ether and 2,2-di(4-nitrophenyl)propane and itshexafluoro analogue since these compounds are easily reduced to theirdi(4-aminophenyl)analogues for use in the polymer industry tomanufacture polyamides, etc.

A number of methods have been devised to synthesize highly regiopuredinitro and diamino compounds but the successful ones are carried out atlow temperature or often begin with regiopure starting materials whichhave been made by costly and time-consuming procedures. See GermanOffenlegenschrift 2,549,036 (5 May 1977) which teaches a 93% selectivityin the nitration of diphenyl carbonate to di(4-nitrophenyl) carbonate at-15° C. to -20° C. It would be of interest therefore to find a methodfor making higher purity di(4-nitrophenyl) compounds directly byimproving the regioselectivity of the nitrating process.

Now it has been found that by carrying out the nitration process ofdiphenyl compounds in the presence of nitrobenzene, not only can theregioselectivity to the para isomer be increased, but the nitration canalso be effected with the improved regioselectivity at essentiallyambient temperature instead of the more usual near-ice temperatures usedin earlier nitrations.

BRIEF DESCRIPTION OF THE INVENTION

The invention described herein is an enhanced regioselective nitrationprocess to nitrate each ring of a compound of formula ##STR1## primarilyin the para position, wherein R is selected from the group consisting of--OCO₂ --, >C(CH₃)₂, >C(CF₃)₂, >CO, >SO₂, >O, >CH₂, >CHR', and >CR'R",and wherein R' and R" are C₁ to C₅ alkyl radicals, to form primarily thedi(4-nitrophenyl) derivative, a process which comprises treating saidcompound in the presence of nitrobenzene at a temperature above about15° C. with a nitrating agent. The invention includes also the use ofthe enhanced nitration process to nitrate 2,2-diphenylpropane which canbe made from alpha-chlorocumene and benzene, and the subsequentreduction of the nitrated product to form an isomeric mixture containingmainly the 2,2-di(4-aminophenyl)propane isomer.

DETAILED DESCRIPTION OF THE INVENTION

The diphenyl compounds useful in this invention are of formula ##STR2##wherein R is selected from the group consisting of --OCO₂ --, >C(CH₃)₂,>C(CF₃)₂, >CO, >SO₂ >O, >CH₂ >CHR', and >CR'R", and wherein R' and R"are C₁ to C₅ alkyl radicals. Preferred are diphenyl compounds wherein Ris selected from the group consisting of --OCO₂ --, >C(CH₃)₂,>C(CF₃)₂, >CO, and >SO₂. Most preferred are diphenyl compounds wherein Ris selected from the group consisting of --OCO₂ --, >C(CH₃)₂, and>C(CF₃)₂.

The nitration process is carried out in solution with concentratednitric acid or a concentrated nitric acid-producing substance inconjunction with a material such as concentrated sulfuric acid ortrifluorosulfonic acid. A mixture of concentrated nitric acid andsulfuric acid is preferred. However, other conventional nitrating agentscan be used, too, as may be understood by one skilled in the art.

The nitration is accomplished in the presence of nitrobenzene as anitration solvent. In general, the amount of nitrobenzene used should bein large excess and keep the diphenyl compound at least mainly insolution. The ratio of substance to be nitrated to nitrating agentshould be between about 0.1 and about 0.6. The ratio does not appearcritical except enough should be used to complete the reaction. Thenitration is carried out preferably at above about 10° C., morepreferably above about 15° C. and, most preferably, above about 17° C.Generally, nitration above a temperature of 30° C. leads to poorer yieldand so a preferred upper temperature limit on the nitration process isabout 25° C. and, more preferably about 20° C.

When the diphenyl compound starting material is diphenyl carbonate thenitration process of this invention can be combined with the isomericpurification technique described in U.S. Ser. No. 292,403, filed Dec.30, 1988, entitled "Changing The Regiopurity of Mixtures Containing4,4'-disubstituted Diphenyl Carbonates," which is incorporated byreference herein.

In this technique the crude di-(4-nitrophenyl) carbonate is mixed withp-nitrophenol and the displaced ortho- and meta-nitrophenols removed bydisplacement and the carbonate optionally decarboxylated. In thisprocess the p-nitrophenol replaced the aromatic rings which are 2- or3-nitrosubstituted and can result in essentially 100% regiopuredi-(4-nitrophenyl) carbonate or ether.

The following Examples will serve to illustrates certain specificembodiments of the herein disclosed invention. These Examples shouldnot, however, be construed as limiting the scope of the novel inventioncontained herein as there are many variations which may be made thereonwithout departing from the spirit of the disclosed invention, as thoseof skill in the art will recognize.

EXAMPLES Example 1

Nitration of diphenyl carbonate in the presence of nitrobenzene.

A 2000 ml reactor equipped with a mechanical stirrer, thermometer, and ajacketed addition funnel was charged with 107.11 g of diphenyl carbonate(0.5 mol) and 500 ml of nitrobenzene. The mixture was stirred untildissolution was complete. In the meantime, the mixed acid reagent wasprepared by mixing 99.02 g of concentrated nitric acid and 125 ml ofconcentrated sulfuric acid in a beaker with cooling. The cooledmixed-acid reagent was then poured into the jacketed addition funnel andfurther cooled with ice. After the diphenyl carbonate had dissolved inthe reaction vessel, the temperature was adjusted to 20° C. with anice/water bath. The mixed-acid reagent was added at a rate whichmaintained the temperature of the reaction mixture at close to 20° C.The total addition took around 60 min. Following the addition, thereaction was stirred for an additional 60 min. The reaction mixture wasthen poured over 600 ml of ice/water. A 600 ml portion of ethyl acetatewas added and the mixture transferred to a separatory funnel and shaken.The organic layer was removed and the aqueous layer was washed 3 timeswith 100 ml portions of ethyl acetate. The organic layers were combinedand washed with 200 ml of saturated sodium bicarbonate and 200 ml ofsaturated brine. The organic layer was then dried over sodium sulfate.

After the reaction mixture was dried, the ethyl acetate was removed byrotatory evaporation. The nitrobenzene solution of crude product waspoured into 2000 ml of cyclohexane and the precipitated crude product(215.16 g) recovered by filtration. Gas chromatography showed theisomeric carbonates to be present in 95.6%, 4,4'-, 0.6%, 4,3'-, and3.8%, 4,2'-dinitrodiphenyl carbonate, amounts. Recrystallization from amixture of toluene and cyclohexane resulted in 142.7 g ofdi(4-nitrophenyl)carbonate or a 94% yield.

Comparative Example 2

Nitration of diphenyl carbonate in the absence of nitrobenzene.

A 1 l reactor equipped with a mechanical stirrer, an addition funnel, athermometer, a condenser and a nitrogen inlet tube was charged with10.71 g of diphenyl carbonate (0.05 mol) and 200 ml of methylenechloride. This was stirred under a slow nitrogen purge until dissolutionwas complete. A 50 g portion of trifluoromethanesulfonic acid (0.33 mol)was added dropwise to the reaction mixture. A 7.7 g portion ofconcentrated nitric acid (0.11 mol) was added dropwise at a rate whichmaintained the temperature at 25°±1° C. Cooling with an ice bath wasused to maintain the temperature. The addition of nitric acid required15 min. Following the addition of the acid, the ice bath was removed andthe reaction mixture was stirred for 1 hr at room temperature. After 1hrthe reaction was quenched by the addition of ice and the solutiontransferred to a separatory funnel and an additional 1 l of methylenechloride added. The aqueous and organic layers were separated and theorganic layer washed with two 500 ml portions of water and sodiumbicarbonate solution. The product solution was dried over sodium sulfateand concentrated to produce 16 g of crude product containing the 4,4'-and 4,2'-dinitrodiphenyl carbonates in a 77 to 23 ratio.

Comparative Example 3

Nitration of 2,2-diphenylpropane in the absence of nitrobenzene.

A 0.98 g quantity of 2,2-diphenylpropane in 10 ml of concentrated H₂SO₄. The mixture was cooled to 17° C. and 0.99 g of concentrated HNO₃added dropwise such that the temperature was held between 17° C. and 20°C. Mechanical stirring was continued for 20 min after which the reactionmixture was added to ice. The product was extracted with methylenechloride which was evaporated to give 1.2 g (86%) of crude product.Selectivity to the 4,4'-disubstituted diphenyl product was 64%.

Example 4

A quantity of 2,2-diphenylpropane was made as follows:

Into a 3 l, three-necked, round-bottomed flask were added 1562 (20.0mols) of dry benzene and 66.67 g (0.5 mols) of aluminum chloride. Thebenzene solution was stirred with a mechanical stirrer under nitrogenatmosphere in an ice-water bath.

Into this benzene solution, alpha-chlorocumene made by HCl addition toalpha-methylstyrene was added slowly over a period of 2 hr through thejacketed dropping funnel with dry-ice and acetone cooling jacket. Afterthe completion of the addition of alpha-chlorocumene, the ice-water bathand the addition funnel were removed. The reaction mixture was stirredfor another 30 min while the temperature was allowed to slowly warm upto ambient temperature.

The orange-colored reaction mixture was then poured into 2 l ofice-water and stirred for 30 min. The organic layer was separated fromthe aqueous layer by a separatory funnel, and dried over anhydrousmagnesium sulfate. The benzene solution was filtered. The volume of thesolution was reduced on a rotary evaporator. The resulting residue wasthen vacuum-distilled to give 335.2 g (1.71 mols) of2,2-diphenylpropane. The yield was 85.4 mol percent.

Example 5

A quantity of 2,2-di(4-nitrophenyl)propane was made as follows:

A 1 l glass reactor equipped with baffles, mechanical stirrer,thermometer, and a jacketed addition funnel was charged with 9.80 g(0.05 mols) of 2,2-diphenylpropane, 100 ml of nitrobenzene, and 12.5 mlof sulfuric acid. The mixture was stirred and cooled in an ice bath.Meanwhile 7.70 g of 90% nitric acid (1.1 mol) and 12.5 ml of sulfuricacid were mixed in a beaker and cooled in an ice bath. The mixed acidwas then transferred to the jacketed addition funnel and maintained coldwith an ice bath. The temperature of the reaction mixture was adjustedto 17° C. and the mixed acid reagent was added to the well stirredreaction mixture at a rate which maintained the temperature at 17° C.With sufficient cooling the addition requires 0.25 hr. AFter theaddition of the mixed acid reagent was complete, the reaction mixturewas allowed to warm to room temperature and was maintained with stirringat room temperature for 1 hr. The reaction mixture was poured onto 300 gof ice. Sufficient methylene chloride was added to completely dissolveany solids present and the aqueous and organic layers were separated.The aqueous layer was extracted with 4 portions (40 ml each) ofmethylene chloride. The combined organic layers were washed with 100 mlof saturated sodium bicarbonate solution and 100 ml of saturated sodiumchloride solution. The resulting wash organic layer was dried overanhydrous sodium sulfate.

A small portion of this solution of the crude product was analyzed byGLC. This analysis indicated a quantitative conversion of the startingmaterial with a selectivity of 82% to the desired material. The dryorganic layer was filtered to remove the hydrated sodium sulfate, andsolvent was removed to in vacuo, resulting in 15.19 g of a yellow solid.

The crude product was recrystallized from 250 ml of ethanol resulting in9.62 g (67.3%) yield of cream-colored crystals (mp 132°-134° C.).

Example 6

A quantity of 2,2-di(4-aminophenyl)propane was prepared as follows:

A 50 ml pressure vessel was charged with 5.0 g of2,2-di(4-nitrophenyl)propane (0.0175 mol), 10 ml of methanol, and 1 g ofa 1% Pd on carbon catalyst. The vessel was assembled and sequentiallypurged with nitrogen and hydrogen. The reactor was pressurized to 400psig hydrogen and then stirred at 2000 rpm. The reaction spontaneouslyheated to 77° C., and was maintained at around 100° C. for 1 hr. Thereaction was cooled to room temperature and removed from the reactor.The catalyst was removed by filtration and the solvent removed in vacuoresulting in 3.82 g (96.6%) of crude 2,2-di(4-aminophenyl)propane (mp123°-125° C.). Analysis by GLC indicated the purity of the material wason the order of 97%.

What is claimed is:
 1. A process to produce 2,2-di(4-aminophenyl)propanecomprising:making 2,2-diphenylpropane by reacting alpha-chlorocumenewith benzene in the liquid phase; nitrating said 2,2-diphenylpropane inthe presence of nitrobenzene at a temperature above about 15° C. toproduce a mixture containing predominantly the2,2-di(4-nitrophenyl)propane isomer; reducing said mixture with hydrogento obtain a mixture predominantly containing2,2-di(4-aminophenyl)propane.